给定一个整数数据流和一个窗口大小，根据该滑动窗口的大小，计算其所有整数的移动平均值。
示例:
MovingAverage m = new MovingAverage(3);
m.next(1) = 1
m.next(10) = (1 + 10) / 2
m.next(3) = (1 + 10 + 3) / 3
m.next(5) = (10 + 3 + 5) / 3
思路：一个队列记录数字，用一个变量记录窗口和即可，每次更新窗口和。
class MovingAverage {int size//窗口大小int windowSum = 0//窗口和int count = 0;//添加数字的次数Deque queue = new ArrayDeque<Integer>();public MovingAverage(int size) {this.size = size;}public double next(int val) {++count;// calculate the new sum by shifting the windowqueue.add(val);//看有没有过期的数字（最左边）int tail = count > size ? (int)queue.poll() : 0;//更新窗口和windowSum = windowSum - tail + val;return windowSum * 1.0 / Math.min(size, count);}
}
/*** Your MovingAverage object will be instantiated and called as such:* MovingAverage obj = new MovingAverage(size);* double param_1 = obj.next(val);*/
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